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import { distinct, distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
import { Directive, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
import { fromEvent, Subscription } from 'rxjs'
@Directive({
selector: '[myInfiniteScroller]'
})
export class InfiniteScrollerDirective implements OnInit, OnDestroy {
@Input() containerHeight: number
@Input() pageHeight: number
@Input() firstLoadedPage = 1
@Input() percentLimit = 70
@Input() autoInit = false
@Input() container = document.body
@Output() nearOfBottom = new EventEmitter<void>()
@Output() nearOfTop = new EventEmitter<void>()
@Output() pageChanged = new EventEmitter<number>()
private decimalLimit = 0
private lastCurrentBottom = -1
private lastCurrentTop = 0
private scrollDownSub: Subscription
private scrollUpSub: Subscription
private pageChangeSub: Subscription
private middleScreen: number
constructor () {
this.decimalLimit = this.percentLimit / 100
}
ngOnInit () {
if (this.autoInit === true) return this.initialize()
}
ngOnDestroy () {
if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
if (this.scrollUpSub) this.scrollUpSub.unsubscribe()
if (this.pageChangeSub) this.pageChangeSub.unsubscribe()
}
initialize () {
this.middleScreen = window.innerHeight / 2
// Emit the last value
const throttleOptions = { leading: true, trailing: true }
const scrollObservable = fromEvent(window, 'scroll')
.pipe(
startWith(null),
throttleTime(200, undefined, throttleOptions),
map(() => ({ current: window.scrollY, maximumScroll: this.container.clientHeight - window.innerHeight })),
distinctUntilChanged((o1, o2) => o1.current === o2.current),
share()
)
// Scroll Down
this.scrollDownSub = scrollObservable
.pipe(
// Check we scroll down
filter(({ current }) => {
const res = this.lastCurrentBottom < current
this.lastCurrentBottom = current
return res
}),
filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
)
.subscribe(() => this.nearOfBottom.emit())
// Scroll up
this.scrollUpSub = scrollObservable
.pipe(
// Check we scroll up
filter(({ current }) => {
const res = this.lastCurrentTop > current
this.lastCurrentTop = current
return res
}),
filter(({ current, maximumScroll }) => {
return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
})
)
.subscribe(() => this.nearOfTop.emit())
// Page change
this.pageChangeSub = scrollObservable
.pipe(
distinct(),
map(({ current }) => this.calculateCurrentPage(current)),
distinctUntilChanged()
)
.subscribe(res => this.pageChanged.emit(res))
}
private calculateCurrentPage (current: number) {
const scrollY = current + this.middleScreen
const page = Math.max(1, Math.ceil(scrollY / this.pageHeight))
// Offset page
return page + (this.firstLoadedPage - 1)
}
}
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